There are many kinds of lighting apparatuses. Many of the most recent ones consist of light emitting diodes (LEDs) as light sources. LEDs are individual light sources, that, when placed in an appropriate housing, can illuminate a space as a recessed “downlight”. Downlights are desirable in both offices and homes and are used as a primarily light source in many applications. Typically, downlights contain both an LED light source and a driver, which is used to provide the proper current/voltage to the LED.
Some downlights are made to be adjustable, which allows the light source to be pointed in a particular direction other than directly downward. Potential uses for this are to highlight a wall or to point downward when the fixture is mounted on a sloped ceiling. Typically, adjustable downlights offer a horizontal rotation of approximately 360 degrees and a vertical pivot of 30-40 degrees. The 360 degree rotation is sometimes achieved by rotating on the horizontal axis just 180 degrees and pivoting the LED 30-40 degrees in both directions, which gives the fixture the full desired adjustability.
Part of a good downlight design includes the ability to easily service the LEDs and drivers. As drivers and eventually LED's can have issues and need servicing, access to both of these are a critical part of a good downlight design.
One recent change in the industry is that plenums (the space between the structural ceiling and the drop down ceiling, which is usually sheetrock) are getting smaller. Perhaps due to the increasing cost of real estate and/or the desirability of increased room heights, less and less space is being allotted to the plenum.
In the past, downlights, especially IC rated (which can be surrounded by insulation, as opposed to non-IC rated fixtures, which require a void of 3″ around the fixture to operate safely) have been as tall as 8″ or more. But due to the recent change in customer demand, manufacturers of downlights have recently adapted by offering shallow downlights with heights of, for example, 4 inches or less. It should be noted that there is no technical or conventional definition of a “shallow” downlight vs. a non-shallow downlight; in other words, there is no authority that defines a shallow downlight as being, for example, less than 4 inches in height.
There are several design challenges in making a shallow downlight. Generally speaking, a fixture is considered aesthetically pleasing for modern lighting designers if it has a regressed lens. That is, the lens that diffuses the light is preferred to be not at the surface of the lower ceiling but rather regressed into the ceiling. The exact placement is likely a matter of taste, but industry standard seems to be around 1 inch regressed, which is provided by a “trim”, which has a regressed horizontal lens (made of solite, glass, or other similar material), diagonal beveled aluminum sides, and, if it is a “flanged” trim, a horizontal flange beneath the ceiling of varying widths (depending on the manufacturer). This desired ˜1 inch space of regression can be offset somewhat by the thickness of the drywall itself, which typically can range from ½″ to 1″.
In addition, some diffusion and beam spreading is required to allow for the light to look aesthetically pleasing to those in the lighted space. A distance (the exact measurement depends on various factors such as the LED source type), is required for the light to diffuse before striking the lens. Also, depending on the application, lighting designers may want a wide beam or narrow beam spread or somewhat in between, which is provided by a beam spread lens or reflector. This prevents the LED light source from being directly above the lens of the trim, but rather regressed even further into the fixture.
A heat sink is needed to dissipate the heat of the LED source or the fixture will get too hot, failing safety tests. Typically, heat sinks are crafted from aluminum and are mounted to the rear of the LED source. In a shallow downlight, there is little room to place a heat sink above the LED. Putting the heat sink to the sides of the LED source, while making sense logistically, is not optimal for thermal distribution using conduction alone, because not enough heat will be drawn from the LED sideways. There would also be a dramatic delta between the heat level of the aluminum closest to the LED and that of the aluminum on the outer edges of the heat sink, which is considered non-optimal in terms of proper heat sink design, regardless of the temperature.
Even if a heat sink is designed that surrounds the main LED source and draws the heat away properly, a novel design for incorporating the driver would need to be created. In a typical downlight design with the heat sink above the LED source, there is usually enough space to the sides of the LED module for an electrician's hand to fit through to allow for driver servicing. But if the entire heat sink mechanism is surrounding the LED source on the horizontal plane, servicing a driver that is located outside of the mechanism would be difficult, because the mechanism would either have to be removed or have an opening, which would reduce the heat sinking properties. And, if the driver was located on the rotating mechanism, a novel approach would have to be taken to avoid the building's line wire from rotating along with the mechanism. Moving line wires coming from the building can cause potential problems as the conduit may not be as flexible as needed by the fixture to do the rotation. Especially where there is limited plenum space, the conduit's flexibility may also be limited by the distance to structural ceiling.
If a fixture is designed that had an LED pivoting on one axis and another mechanism (such as a heat sink) rotating on another axis, there would need to be a limited number of parts involved in the transfer of heat. Each additional part creates another point of thermal conduction; each point of thermal conduction creates a substantial loss of thermal conductivity.
Creating a shallow housing downlight that is adjustable is even more difficult than a static downward-facing downlight, as the mechanisms for the approximately 360 degree rotation and the 40 degree pivot both need to be operate within the limited space.
Some of the leading manufacturers of downlights have offered shallow housing for non-adjustable applications, as shallow as 2″ depth, using custom designed aluminum heat sinks that move the heat away from directly above the LED source. But, shallow adjustable downlights are scant in today's market and those that exist are currently 3.5″ or taller.